1. Field of the Invention
The present general inventive concept relates to an optical reading document board, an image reading apparatus, and an image forming apparatus including the image reading apparatus.
2. Description of the Related Art
In image reading apparatuses, such as copy machines, facsimiles, and scanners, an image sensor reads image information by receiving light reflected from a document, and converts the image information into an electric signal.
Such image reading apparatuses include a light source for generating light, the image sensor for receiving light reflected from a document and converting the light into an electric signal, and a reflector disposed to form an optical path between the light source and the image sensor. Generally, the light source may be a line source, such as a cold cathode fluorescent lamp, or a xenon lamp.
In the image reading apparatuses, the light source is disposed near the document, and thus the light reflected from the document is reflected by an optical reading document board, which is formed of flat glass and on which the document is placed, and is incident again on the document.
As such, when the light reflected from the document is incident again on the document by being reflected by the optical reading document board, illuminance of a portion of the document on which the light is incident again is increased, and thus the document is read to be falsely brighter than it is.
Since a general refractive index of a flat glass plate is about 1.5, reflectance at each interface of the flat glass plate is about 5% and reflectance of the top and bottom surfaces of the flat glass plate is about 10%. Accordingly, the reflectance by the flat glass plate is also about 10%. Thus, by reducing the reflectance at the corresponding interface of the flat glass plate, the secondary reflection may be reduced to a predetermined amount.
Consequently, a method of reducing the secondary reflectance at an optical reading document board is needed to be studied.